Conventionally, as shown in FIG. 5, a piezoelectric actuator 1 is constituted in such a manner that thin piezoelectric plates 5 and 7 are stuck to opposing faces of rectangular conductive plates 3, and electrodes 5a and 7a are disposed on the opposing faces which are not brought into contact with the plates 3 in each piezoelectric plate 5, with the plates 3 serving as common electrodes, and while supporting one end (left end in the figure) in the longitudinal directions of the plates 3 in an open-sided shape, the other end (right end in the figure) is formed in an open end. Note that a support member of the piezoelectric actuator 1 is not shown in FIG. 5 (see FIG. 6).
In the piezoelectric actuator 1, for example, when positive potential+is applied between a positive terminal P1 and a common terminal P3 (between the electrode 5a of the piezoelectric plate 5 and the plate 3) according to the polarization directions of the piezoelectric plates 5 and 7, for example, the plate 3 is bent so that the open end is displaced in the upward direction as shown by broken line in FIG. 5.
Meanwhile, when a negative potential—is applied between the common terminal P3 and a negative terminal P2 (between the plate 3 and the electrode 7a of the other piezoelectric plate 7), for example, the open end is displaced in the downward direction as shown by one-dot chain line in the figure.
Then, the piezoelectric actuator 1 is used as various driving sources, such as a needle selecting driver of knitting needles of a knitting machine, by utilizing a bending motion by dint of such a piezoelectric phenomenon.
Specifically, as shown in FIG. 6, the aforementioned plural piezoelectric actuators 1 (shown by dividing into 1a, 1b, 1c, 1d, 1e, 1f, 1g, and 1h in the figure) are arranged on a side wall 9a in a long and narrow insulating box-shaped case 9 in parallel to each other at prescribed intervals apart from one another, with the one end supported in an open-sided shape and the other end as the open end inserted into operation holes 11 formed on the side wall 9b opposing to the side wall 9a in the case 9 with a certain play. Then, operation pieces 13 as mechanical components fixed to the other ends are protruded with a certain play from the operation holes 11.
A plurality of piezoelectric actuators 1a to 1h (including the operation pieces 13) supported by the case 9 are the same actuators, and FIG. 7 is a view of the case 9 viewed from the side of the side wall 9b of the case 9, specifically from tip end sides of the operation pieces 13.
When a positive/negative direct current drive voltage is applied from a power supply section 15 to such plural piezoelectric actuators 1a to 1h through a controller 17, each of the piezoelectric actuators 1a to 1h is bent and the operation pieces 13 protruding from the operation holes 11 of the case 9 are displaced. This contributes to moving a selecting needle lever not shown (mechanism component) by the operation pieces 13.
Then, when the controller 17 switches and selects the drive voltage applied to the plural piezoelectric actuators 1a to 1h, the piezoelectric actuators 1a to 1h can be used as a needle selecting driver of the knitting needles of the knitting machine, for example.
A general patent document according to such a kind of piezoelectric actuator includes a patent document 1 (Japanese Patent Laid Open No.5-302251).
Further, the structure as shown in FIG. 8 is given as an example of the structure of controlling the drive voltage applied to the plural piezoelectric actuators 1a to 1h by the controller 17.
Specifically, phototransistors Q1 and Q2, Q3 and Q4, Q5 and Q6, Q7 and Q8, which are connected in series respectively, are disposed corresponding to the plural piezoelectric actuators 1a to 1h. A collector of one of the phototransistors Q1 is connected to phototransistors Q1 and Q2 through a resistor R1 from a positive side feeder line 19, and an emitter of the other phototransistor Q2 is connected to a negative side feeder line 21 through a resistor R2.
The positive terminal P1 in the piezoelectric actuator 1a is connected to the positive side feeder line 19, the negative terminal P2 is connected to the negative side feeder line 21, and joints of the phototransistors Q1 and Q2 are connected to common terminal P3 of the piezoelectric actuator 1a. 
Similarly, the phototransistors Q3 to Q8 are also connected to the positive side and negative side feeder lines 19 and 21 through resistors R3 to R8, and the piezoelectric actuators 1b to 1d are also connected to the joints of the phototransistors Q3 to Q8 and the positive side and negative side feeder lines 19 and 21.
In addition, light emitting diodes D1 and D2, D3 and D4, D5 and D6, and D7 and D8 are disposed in proximity to and corresponding to the photo transistors Q1 and Q2, Q3 and Q4, Q5 and Q6, and Q7 and Q8 connected in series.
The light emitting diodes D1 to D8 are emitted by selectively energizing by a switching control section 23, and the driver of the aforementioned piezoelectric actuators is thereby formed.
In FIG. 8, the aforementioned controller 17 is formed by the phototransistors Q1 to Q8, light emitting diodes D1 to D8, and the switching control section 23.
Note that in FIG. 8, the light emitting diodes D1 to D8 are connected by one line from the switching control section 23. However, actually the light emitting diodes D1 to D8 are connected by individual wiring corresponding to the light emitting diodes D1 to D8. Such wiring is simplified in FIG. 8 so as to be easy to understand.
Then, for example, when the piezoelectric actuator 1a out of the plural piezoelectric actuators 1a to 1d is on-operated, the open end is displaced in the upward direction through the conduction control of only light emitting diode D1 selectively by the switching control section 23. Meanwhile, the tip end is displaced in the downward direction through the conduction control of only light emitting diode D2 selectively.
Similarly, in the other piezoelectric actuators 1b to 1d also, the tip end is displaced through the conduction control of only either of the light emitting diodes D3 or D4, D5 or D6, and D7 or D8.
In the driver of the piezoelectric actuators thus constituted, the resistors R1 to R8 connected between the phototransistors Q1 to Q8 and the positive side and negative side feeder lines 19 and 21 have a current limit function to suppress a drive current flowing through the phototransistors Q1 to Q8 so as not to increase the power consumption for the entire driver due to increased drive current, which occurs when one of the phototransistors is switched to the other in the phototransistors Q1 and Q2, Q3 and Q4, Q5 and Q6, and Q7 and Q8, thereby causing both of the phototransistors Q1 and Q2, Q3 and Q4, Q5 and Q6, and Q7 and Q8 to be temporarily conducted or a rapid current change to occur, resulting in a large drive current.
However, in the driver of the aforementioned piezoelectric actuators, the resistors R1 to R8 for current limitation are connected to the plural phototransistors Q1 to Q8 to on-drive the plural piezoelectric actuators 1a to 1h. Therefore, the number of components is increased, the wiring is complicated, a cost is difficult to be reduced, and productivity is also difficult to be improved.
In such a condition, it is considered that if the resistors for current limitation are inserted in the parts up to the controller 17 one by one in the positive side and negative side feeder lines 19 and 21, the number of components is reduced, and the wiring is simplified. However, this is not realized for the reason described hereunder.
More specifically, in the piezoelectric actuators 1a to 1h of this kind used for the needle selecting driver of the knitting needle of the knitting machine or the like, a quick switching speed allows the knitting needle to be quickly displaced, thereby increasing a knitting speed.
For example, when the piezoelectric actuator 1a is on-controlled and another piezoelectric actuator 1b is on-controlled at the same time or immediately following, or when the piezoelectric actuators 1a to 1h are sequentially on/off controlled while on/off operation switching timing is reduced, a large drive current flows temporarily. Under such a situation, if one or a pair of resistors R for current limitation are provided, heat generation is apt to be large.
In order to avert above-described situation, a large power consumption and an expensive resistor are needed, and consequently, inexpensive resistors R1 to R8 with low power consumption are inserted and connected for each of the piezoelectric actuators 1a to 1h. 
The inventors of the present invention carefully study on the function and an equivalent circuit of the piezoelectric actuators 1a to 1h. As a result, the inventors of the present invention focus on the point that the piezoelectric actuators 1a to 1h have a function as capacitors equivalently, and the drive current flowing through the piezoelectric actuators 1a to 1h is reduced in accordance with the progress of charging operation, although large immediately after the on-control, and after a specified period has passed, the drive current becomes very small, and the change with the lapse of time is small. Consequently it is found that the number of the resistors is reduced and the piezoelectric actuators 1a to 1h can be switched at a high speed, and the present invention is thus completed.
In order to solve the above-described problem, an object of the present invention is to provide a driver of a piezoelectric actuator capable of reducing in the number of resistors suppressing increase in a drive current and switching plural piezoelectric actuators at a high speed and sustaining low power consumption for the entire driver in the driver for driving the plural piezoelectric actuators.